The present invention relates to a dialysis machine having a proportioning device for supplying dialysis fluid for a dialysis treatment and a method of operating a dialysis machine.
To prepare dialysis fluid today it is customary in most cases to use prefabricated dialysis concentrates that need only be diluted with an appropriate amount of water. To avoid removing heat from blood during dialysis, the dialysis fluid is heated to body temperature. Furthermore, air dissolved in the dialysis fluid is removed by degassing.
The operation of mixing water and concentrate in a certain quantity ratio is referred to in general as proportioning. There are known proportioning devices where the metering is based not on a predetermined volume ratio but instead on reaching a certain electric conductivity in the resulting mixture. For conveying water and concentrate, proportioning devices that operate according to conductivity have pumps whose flow rates are regulated as a function of the measured conductivity to yield a dialysis fluid having the desired composition.
Because of the large exchange volumes, there is a need for accurate balancing of the fluid removed and the fluid supplied over the entire treatment period with the known dialysis machines. Volumetric balancing machines are state of the art.
German Patent Application 28 38 414 A discloses a dialysis machine having a volumetric balancing system. The balancing system is made of two chambers subdivided by a movable partition, each having an inlet line for fresh dialysis fluid and an outlet line for spent dialysis fluid. Cutoff valves controlled by a control unit are arranged in the inlet and outlet lines. The balancing system is operated in such a way that fresh dialysis fluid is alternately supplied to the two balancing chambers from one dialysis fluid source and spent dialysis fluid is removed at the same time.
To prepare the dialysis fluid with the known dialysis machines, water is generally mixed with one or more concentrates in a reservoir. The addition of concentrate takes place in accordance with the cycle of the balancing chamber of the balancing system, while the addition of water is regulated by a liquid level sensor in a reservoir that controls the water inlet valve as a function of the liquid level in the reservoir. If there is a change in flow rate, the proportioning becomes less accurate. Changes in flow rate occur, for example, in filling programs when a great deal of gas is produced in degassing the fluid coming from the dialyzer, or when there is a change in the hydraulic resistance in the tubing lines. These factors cause a change in the cycling of the concentrate pumps, but the water supply remains almost unaffected by this. These factors can lead to a change in the water-concentrate mixing ratio. In addition, these changes in pressure and flow have an effect on the injection points of the concentrates, which can also lead to problems in proportioning.
German Patent 30 06 718 describes a dialysis machine in which the proportioning of the dialysis fluid is accomplished by the balancing chamber of the balancing system. Therefore, concentrate is added when filling the chamber with fresh water.
The object of the present invention is to create a dialysis machine having a proportioning device for supplying dialysis fluid that will allow proportioning with a high accuracy regardless of flow rates. Another object of the present invention is to provide a method with which dialysis fluid can be proportioned for a dialysis machine with a high accuracy.
In one embodiment of the invention a dialysis machine is provided that includes a dialyzer subdivided by a semipermeable membrane into a chamber for a liquid to be purified and a dialysis fluid chamber. A dialysis fluid inlet line lead to an inlet of the dialysis fluid chamber. A dialysis fluid outlet line leads away from an outlet of the dialysis fluid chamber. A balancing system is also provided and is connected to the dialysis fluid inlet and outlet lines for balancing fresh and spent dialysis fluid. Also included is a proportioning device for supplying fresh dialysis fluid. The proportioning device includes a water source and at least one proportioning unit. The proportioning unit has a first chamber half and second chamber half configured to operate so that liquid is displaced from one chamber half when the other chamber half is filled with liquid. An inlet line leads from the water source and connects to an inlet of the first chamber half and an inlet the second chamber half. An outlet line connects to an outlet of the first chamber half and an outlet of the second chamber half. This allows the chamber halves to be alternately filled and emptied. At least one mixing point is provided in the inlet line or the outlet line. At least one dialysis fluid concentrate source supplies a fluid concentrate to a mixing point for forming a fresh dialysis fluid. An equalizing chamber is provided for the fresh dialysis fluid. The equalizing chamber is connected to the outlet line.
This invention makes it possible to separate the addition of concentrate from the balancing of dialysis fluid added and removed. The proportioning device can be installed in the known dialysis machines without any great changes in the equipment design. However, it may also form an independent unit, which is connected to a dialysis machine.
The advantages of this invention include the fact that a concentrate or more than one concentrate is/are always added at a certain flow rate regardless of which dialysis fluid flow rate is set. Since the concentrates and water are always mixed at a certain flow rate, the concentrate and water can be proportioned accurately to achieve a certain conductivity.
The flow rate is set by alternately filling the first and second chamber halves of a proportioning device, such that when filling one half of the chamber, liquid is displaced from the other half of the chamber. The flow rate is based on the volume of the chamber halves and the filling time and emptying time, which can be set with precision by switching cutoff elements arranged in the inlet and outlet lines of the chamber halves.
The proportioning device may include just one proportioning chamber which is subdivided by a movable partition into two chamber halves. However, each chamber half may also be part of its own separate proportioning chamber, each having a separate displacement element coupled together so that liquid is displaced from one half of the chamber when filling the other half.
Since ready-made dialysis fluid is supplied, the design of the actual balancing system is simplified inasmuch as it is not necessary to mix water and concentrate(s) by using the balancing chambers of the balancing system.
The dialysis fluid may be prepared by mixing one or more concentrates and water, with the water and concentrates being mixed at one or more mixing points. The mixing points may be located upstream or downstream from the proportioning device. The composition of the mixture of water and concentrates may be monitored by being measured downstream from the respective mixing point. This can be accomplished by a conductivity measurement or by a density measurement.
The water flows during proportioning if a concentrate has not yet been added or the mixture of water and concentrate(s) always has a preselected flow rate regardless of other influences. Thus, only the pauses between switching the chamber halves of the proportioning device depend on the flow of dialysate.
To be sure that a sufficient volume of dialysis fluid can be supplied, the ready-made dialysis fluid is collected. This makes it possible to perform the proportioning in successive cycles.
In a preferred embodiment, to supply a certain reservoir of fresh dialysis fluid, a liquid level indicator and a control unit are provided, so that after the liquid level drops below a predetermined setpoint, the proportioning device switches, causing a certain volume of liquid to be conveyed in cycles at a predetermined flow rate.
The ready-made dialysis fluid is preferably collected in an equalizing chamber that may have an inlet for supplying the ready-made dialysis fluid and an outlet for removing same, the dialysis fluid preferably being conveyed into the balancing system by means of a pump connected to the supply line. Since the balancing system does not convey liquid continuously but only in cycles, a recirculation line, preferably with a pressure relief valve connected to it, branches off from the supply line. If a certain excess pressure builds up in the supply line, the excess dialysis fluid can be recirculated.
A vent opening is preferably provided above the liquid level in the equalizing chamber, so that gas (dissolved or undissolved) entrained with the dialysis fluid is automatically separated. Thus, additional air separators can be omitted in principle.
The concentrate or the individual concentrates are preferably supplied in containers, e.g., canisters or bags to which concentrate lines leading to the individual mixing points are connected. However, it is also possible for the concentrates to be supplied from a central concentrate supply.
Water for preparing the dialysis fluid is preferably degassed and/or heated before entering the balancing chamber. The degassing and heating unit remains free of concentrates except in rinsing operations or in emptying the concentrate bags.